Electrochemical energy sources in which seawater and/or an alkaline solution is usable as electrolyte are suited for a number of applications. Examples have been ships and other watercraft, electronic devices, toys and the like, and highly promising future applications can been seen on a large scale in the growing field of renewable energies. Various types of so-called seawater cells are known, which use seawater as electrolyte and which comprise a number of basic components, especially a cathode and an anode. One of the known types of a seawater cell is a magnesium/oxygen battery comprising a magnesium anode, which utilizes seawater as electrolyte as well oxygen dissolved in the seawater as oxidizing agent.
The chemical processes taking place in this cell are the following:
On the anode, magnesium is dissolved according to the equation2Mg=2Mg2++4e−. 
On the cathode, oxygen is consumed according to the equationO2+2H2O+4e−=4OH—.
Summarizing, this can be described in a simplified manner as follows:2Mg+O2+2H2O=2Mg(OH)2.
The anode material can be, for example, magnesium, zinc, a mixture of these elements and alloys thereof.
U.S. Pat. No. 4,822,698 discloses an energy cell/battery for use in seawater. This battery works according to the aforementioned electrochemical reactions, with magnesium or zinc being used as anode material and an oxygen electrode as cathode. The oxygen supplied to the cathode is dissolved in the seawater. This seawater battery consists of a cylindrical oxygen electrode cathode. The structure comprises single or several anode rods, which contain magnesium or zinc. The oxygen electrode is similar to those used in many ways in other batteries, e.g. in U.S. Pat. No. 6,372,371 B1. In seawater saturated with air, the disclosed battery is capable of supplying approximately 1.5 volt with 50 mA. The cathode has a size of approximately 800 cm2. The battery has a relatively small energy density of about 1 W/m2.
U.S. Pat. No. 5,405,717 discloses a seawater cell, the power of which is slightly increased as compared to that of U.S. Pat. No. 4,822,698. This power increase is caused by the effect of waves, which increases the flow of the seawater through the cathode so as to supply oxygen. The cell structure includes water flow conducting means, which make the water flow through the cell. U.S. Pat. No. 5,225,291 discloses a seawater battery, which is operable with or without dissolved oxygen due to the use of a hybrid cathode. U.S. Pat. No. 5,427,871 relates to galvanic seawater cells and batteries, respectively, which use oxygen dissolved in the seawater as oxidizing agent.
Another galvanic type of seawater batteries, in which normally seawater is used as an electrolyte, comprises a magnesium anode and a cathode of copper chloride or silver chloride. These long-term batteries do not need oxygen dissolved in seawater, but they have a small output energy density, are generally heavy and require much space. A Mg/CuCl battery with a watt-year as output energy may have a length of 8½ feet, a diameter of 9 inches and a weight of approximately 100 pounds. Moreover, these batteries have a limited flexibility with respect to the design and are restricted to a longitudinal shape. Examples are described in U.S. Pat. Nos. 4,601,961, 5,288,564, or U.S. Pat. No. 6,656,628 B2.
Metal-air cells may be primary cells, comprising an anode made of metal, e.g. of aluminium, magnesium or zinc, and an air cathode, which is disposed with a small spacing from the metallic anode, but does not touch the same. A suited electrolyte is provided in a space between the cathode and anode. The anode is immersed into the electrolyte. Different embodiments of such batteries and methods for the production and use of such batteries are known from the prior art, compare, for example, U.S. Pat. Nos. 5,004,654, 5,360,680, 5,376,471, 5,415,949, 5,316,632. Typical metal-air batteries and metal-air fuel cells, respectively, are described, for example, in U.S. Pat. No. 6,127,061.
Besides their use in the above-referenced electrical energy generators, magnesium or electrochemically related metals and their alloys, placed in aqueous solutions, have been used to generate hydrogen, which is being considered as an important energy source of the future. Basic concepts in this regard have been developed by Pacheco, e.g. in U.S. Pat. No. 6,834,623. In JP 2003 221 201 A hydrogen generating device is disclosed, which contains magnesium alloy particles consisting of granular magnesium and a plurality of catalytic nickel or iron particulates on the surface and at the inside of the granular magnesium in a closed reactor vessel.